The present invention relates to a stopper to close bottles which is particularly adapted to store and age vintage wines and is made of synthetic material.
It is well known that wine bottling, more particularly of expensive and consequently valuable wines involves use of glass bottles and corks.
Corks are specially used to store and age vintage wines because cork allows a limited exchange of oxygen between the bottle interior and the ambient and viceversa. This is the essential condition in order that wine can mature and get refined without deterioration of the wine.
Not all corks can be used to bottle vintage wines and this depends both on quality of cork and the cork production system. Indeed corks made for instance with cork granules joined by an adhesive are not adapted to warrant the correct permeability allowing passage of the required but minimal quantity of oxygen to age and refine wine.
Another drawback of the corks is the possibility that the cork may keep even after manufacture mould or residues giving a sharp and intense taste to wine, called cork taste.
Another drawback of the cork consists in that when bottling the cork should have an average moisture not less than 5% and no more than 8%, because a low moisture lower than 5% would cause a too high exchange of oxygen with the ambient while a too high moisture could develop mould.
If on one hand vintage wines need corks of high quality for their storage and ageing, on the other hand the world production of cork more particularly of high quality, is insufficient to meet the demand of the market of vintage wines.
For this reason in the recent times stoppers made of synthetic material were developed, for instance, of polyethylene resins added with a suitable expansion agent, which on one hand can be used to store vintage wines for short periods of time, but on the other hand they are not suitable for their ageing.
Indeed the stoppers made of synthetic materials allow storage of wine unimpaired relative to the bottling time: wine keeps well its liveliness and freshness without alteration with time, but cannot certainly age because permeability of the synthetic material constituting the stopper reduces the permeability index from 80 to 1000 times in comparison with cork.
The stopper of synthetic material has however several advantages such as to be mould-proof and bacteria-proof, making the bottled wine exempt from cork taste.
Another advantage of the synthetic stopper is constancy of quality of said stopper, durability, flexibility and impermeability to liquids.
One of the limitations of the synthetic stopper is not to allow a correct exchange of oxygen with the ambient in view of its substantial impermeability.
To this purpose it is to be noted that another limitation of the synthetic stopper consists in that it resists hardly the big temperature difference which a bottle of wine may undergo for instance when left temporarily in the sun, because increase of volume of wine inside the bottle and the substantial impermeability of the synthetic stopper does not allow leakage of an amount of air comprised between the wine level and the bottom portion of the stopper. Consequently phenomena of stopper removal from its seat and movements of the stopper upwards or even ejection from the bottle were observed.
FR-A-2627467 discloses a flotting cover in a vat of liquid provided with a stopper having a tubular duct having a membrane arranged transversally at the end of said duct. Said membrane allows the passage of the entrapped gasses to escape from the interior of the vat to the outer ambient.
The object of the invention is to provide a stopper of synthetic material overcoming the above mentioned drawbacks.